| Meta-surfaces with sub-wavelength structural dimensions have shown broad prospects in the field of optics and microelectronics due to their powerful electromagnetic control capabilities.In the radio frequency and microwave frequency bands,etching the metallic surface into properly designed periodic structure will generate surface waves.It replaces the coupled resonance of free electrons and incident electromagnetic waves on the traditional structure through structural resonance,mimicking the so-called surface plasmon in the optical frequency band.The collective oscillation phenomenon of free electrons on the metal surface brings forward the concept of spoof surface plasmon.In particular,the localized spoof surface plasmons have high localized field enhancement and field confinement properties.In this paper,a space-filling curve-based meta-surface is proposed and a series of studies were done on its surface electromagnetic properties.The main contents and achievements of the research are summarized as follows:A subwavelength cross-comb space-filling meta-surface was designed by using metal curves,and a series of studies on spoof localized surface plasmons were carried out on this basis.Theoretical analysis and calculation were carried out according to the structural characteristics.The curved arrangement of the metal will form an air waveguide.Under the excitation of the incident electromagnetic wave,spoof localized surface plasmon like Fabry-Perot resonance will be generated,and the resonant frequency of the meta-surface can be calculated.Using the finite element method to simulate the 2D comb structure with different periods,it is found that the Q-factor of1.7×10~5 can be obtained when the structure compression ratio(λ/L)is 444 by adjusting the structure period.When studying the higher-order eigenmodes of the comb-shaped space-filling curved structure,it is found that the spoof localized surface plasmons supported by the structure are alternately supported by magnetic multipoles and electric multipoles.The scattering cross sections are presented at equally spaced frequencies,and the excitation of eigenmodes by incident plane waves of different polarizations is also different.Changing the distribution type of the space-filling structure shows that the surface plasmon resonance properties supported by it are not affected by the arbitrary tortuosity of the structure,and the magnetic field strength distribution of the eigenmodes only changes with the orientation of the air waveguide.The 3D simulation of the cross-comb-shaped space-filling structure was also carried out.From the electric field diagram of the X-Z section,it can be observed that the spoof localized surface plasmons generated by the structure can bind the energy to the surface of the structure and generate localized field enhancement.The results of the research on the annular helical structure show that the effect of local field enhancement can be changed by adjusting the hollow ratio of the structure.The fabrication of ultra-thin space-filling meta-surfaces is accomplished by UV exposure lithography and electron beam evaporation metal coating.A metal film with a thickness of 500 nm was prepared on a quartz substrate by a double-layer positive photoresist process.This process is convenient and simple,and can achieve high-precision,large-area,and low-cost sample preparation.The experimental detection of the helical space-filling structure is carried out by building a near-field electromagnetic detection instrument,which is basically consistent with the simulation results.The study of the physical mechanism of space-filling meta-surfaces can provide new ideas for the construction of spoof localized surface plasmons and the design of small integrated circuit systems in the microwave frequency band.The surface has excellent field localization and high Q factor characteristics.It can also exert great application value in the construction of compact high-performance resonant elements and integrated systems. |
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